As both frequencies increase and energy content grows in inductors they are usually produced using e.g. 1) laminated steel plates with different thicknesses i.e. 0.5 mm 0.35 mm, 0.22 mm, 0.10 mm, depending on frequencies, 2) amorphous magnetic material, 3) sintered ferrite or pressed Soft magnetic composite (SMC) materials made into E, C or U shaped cores or I or toroid shaped cores, which can be glued together to make larger units and pot cores. A common problem with all these technologies is that introducing effective liquid cooling into their structure results in considerable mechanical challenges. Liquid cooling technologies usually entail numerous connecting points creating leakage risks as well as additional production steps. Another problem is that cooling both the conducting wire and the core material simultaneously with known and simple methods such as using planar liquid or air cooled heat sinks is very challenging or impossible. Furthermore, due to the fact that these units are produced from standard core materials the possibilities for optimization are limited. Also, due to challenges in production, some shapes made from pressed materials are not available above certain sizes. Additionally, inductors made with said technologies do not have a direct thermal connection between the core and coil material and their mechanical structure is such, making it impossible to create fully thermally homogenous designs. This creates inefficiencies and weaknesses in the inductor's structure.
The main technical challenge with inductors that have the coil encapsulated within their structure, e.g. pot cores or soft magnetic mouldable material cores, is that the resistive and high frequency related losses stemming from the coil are encapsulated within the inductor's structure. Higher temperature in turn increases the conductor's resistivity affecting its temperature and losses further. High frequencies also give rise to skin—and proximity effect within the coil, increasing temperature and losses in the coil even further.
Coils which are encapsulated within traditional pot cores are usually wound on standard bobbins. As such bobbins usually have very low thermal conductivity this creates a thermal barrier towards the top, bottom and centrum within such inductors. Pot cores are either made into half open cores to allow air cooling of the coil or they are open where the connecting cables come out. In the latter case they are usually filled with thermally conductive polymer based materials to obtain better thermal properties compared to only air. However, thermal properties of such materials are always relatively low in thermal conductivity usually not exceeding 1.5 W/m*K.
Other thermally motivated inductor designs include using aluminum housing for the inductors which are subsequently filled with similar thermally conductive polymer based material as described above. Such inductor designs include C-, U- or E cores, based on different core materials, where the coil is wound on a standard bobbin and subsequently placed between two cores, which usually have discrete air gap in between. The coil or the core is then placed against the aluminum housing which is usually mounted on or connected to a heat sink. Some of such designs also include the inclusion of cooling pipes for water cooling. The problem with these designs is the same as described above. They are not thermally homogeneous in their design. There is no direct thermal coupling between the coil and the core material allowing thermal conduction. The thermally conductive “potting material” has relatively low thermally conductive properties. There is only the possibility of placing either the coil or the core material against the housing/cooling. If such inductors are liquid cooled, this entails complicated mechanical challenges to effectively implement such cooling into their structure. Liquid cooling would further usually call for numerous connecting points creating leakage risks as well as additional production steps. An additional and important drawback is the need for the additional and costly aluminum housing and potting material around the inductor which also adds weight and takes more space within the further technical product.
It becomes particularly important for inductors that have the coil encapsulated within their structure, i.e. pot cores or soft magnetic mouldable material cores, to apply a system that secures the possibility of making inductors that do not run to hot i.e. a system that extracts the heat generated by the losses created in the conducting wire in the most efficient way. If this is not done the units become overly large, heavy and costly. In some cases, i.e. above certain energy content, such inductors become practically impossible to make using the current state of art.